The method and system disclosed herein, in general, relates to information communication. More specifically, the method and system disclosed herein relates to communicating multiple channels of distinct data, simultaneously, over a same frequency using linear polarized signals.
A “frequency band” is a continuum of frequencies usually defined by a higher frequency bound and a lower frequency bound. Typically electromagnetic signals carrying information occupy a narrow frequency band, sometimes also referred to as channels, but may occupy multiple channels or an extremely wide band. Two signals of the “same frequency” means that at least one of the frequencies in the frequency bands used to transmit said two data signals is the same for both signals, i.e., at least part of the band of frequencies overlaps. To be on a “same frequency”, both data signals can occupy the same band or partially overlapping bands. The data signals can convey digital or analog information. As used herein, “data signal” refers to an electromagnetic signal modulated to carry information of any kind.
The “transmit axis” is a line between a transmitting antenna and a corresponding receive antenna. In this invention, multiple data signals and inverted data signals are transmitted at various rotations around the transmit axis.
Linear signals are typically transmitted in one of two rotations, vertical or zero degrees rotation, and horizontal representing an orthogonal, i.e. a 90°, rotation from the vertical around the transmit axis. If two different linear data signals are transmitted on a same frequency they do not interfere when they are transmitted orthogonally to each other. Since there are only two orthogonal linear polarizations, horizontal and vertical, generally the maximum number of signals that can be simultaneously transmitted on the same frequency is two. Transmission of two orthogonal signals on a same frequency is considered frequency reuse since two signals occupy the same frequency simultaneously. This disclosure describes a method to transmit three or more distinct data signals on a same frequency simultaneously resulting in an increase in capacity.
Another form of frequency reuse is through separation. Additional channels can be transmitted on the same frequency as long as there is sufficient distance between the transmitters so that antennas can pick up the selected transmissions with minimal interference. In the case of satellites, the satellites must maintain a distance of about two degrees of arc before the same frequencies can be reused. In the case of broadcast television, terrestrial microwave radios, and for commercial radio stations geographic distance of many miles is used to ensure sufficient attenuation between the transmitters.
Another form of reuse is directional separation caused by use of directional antennas. For example, one tower can hold several directional antennas each pointing in a different direction. Each antenna carries different data signals on the same frequencies. Because of the directionality of each antenna, only signals on the front side of the antenna can be received or picked up. This technique is often used in cell phone communications to accomplish frequency reuse, thereby increasing capacity in a cellular system.
A goal of signal engineering is to maximize the amount of signals carried on the same path and same frequency. This invention achieves this goal by increasing the capacity in any electromagnetic system using polarized waves. The transmission schemes of this disclosure apply to any frequency electromagnetic waves that can be polarized including, for example, light, microwave, and radio frequency waves.
Electromagnetic waves do not interact when transmitted through a non absorbing media such as space. Horizontal and vertical linearly polarized data signals do not modify each other once transmitted and pass through space without interacting. An antenna receives or essentially samples all transmissions passing through a particular point in space at a particular time.
When measuring power around the transmit axis of a single linear polarized signal the formula for off axis power is P1=P·COS φ where P is the power of a specified signal transmitted linearly, φ is the absolute rotation of a receive linear feed in relationship to the rotation of the transmit linear feed, P1 is the power at that angular rotation from the transmitted signal being measured. P1 does not include propagation losses, but represents the received energy of a perfectly aligned receive antenna in relationship to a rotated receive antenna. The power of a linear signal at a rotation of 0 degrees is one, meaning no loss due to rotation, and at 90 degrees, i.e. orthogonal, is zero since COS 90 is 0.
A basic principle of electromagnetic waves is the principle of linear superposition: “when two or more waves are present simultaneously at the same place the resultant wave is the sum of the individual waves.” Physics 3rd Edition by Cutnell/Johnson, Wiley and Sons, 1995.ISBN 0-471-59773-2, page 521.
An inverse signal is a duplicate signal to a first signal, just 180° out of phase. Two inverse signals transmitted cancel each other at reception when they are received together and their amplitudes are equal, and partially cancel each other if there amplitudes are not equal. The disclosed method uses cancellation of inverse signals.
In this invention a first data signal is transmitted in a linear polarization. The signal is characterized by its rotation around the transmit axis (its polarization), by its path of propagation, by its bandwidth, by its power, and by its modulation.
This invention makes use of signals inverse to a first data signal, each transmitted on a side of, i.e. rotated from, said first transmitted data signal, said signals being exactly inverse to said first data signal and at a specified power level in relation to said first data signal. The power levels of the inverse signals are such that they cancel said first data signal at zero degrees rotation from said first data signal, resulting in the reception of an inverse first data signal at a 90 degree rotation from the transmitted first data signal.
An additional quantity of differing data signals are transmitted, rotated around the transmit axis by 180/N degrees, where N is a positive integer representing the total number of desired signals on the same frequency. Inverse signals to each data signal Si are transmitted at ±180/N or less degrees from each data signal Si where i varies from 1 to N.